For example, in an automotive field, springs (volute springs, spiral springs, leaf springs, and the like), to which pulsating bending load is applied, are used, and in these springs, weight reduction and space saving are required. For example, it is proposed that fiber reinforced plastic springs (hereinafter simply referred to as “FRP springs”) be used instead of metallic springs in order to realize weight reduction.
For example, technique of Patent Document 1 discloses an FRP tapered leaf spring as an FRP spring. In this technique, glass fiber or carbon fiber is impregnated into plural pieces of sheet which are different from each other in length, and the plural pieces of sheet are laminated, so that an FRP tapered leaf spring is produced. Technique of Patent Document 2 discloses an FRP leaf spring as an FRP spring. In this technique, a leaf center portion is made of carbon fiber, and a leaf surface portion is made of glass fiber, so that a flexible FRP tapered leaf spring is produced.
Patent Document 1 is Japanese Examined Patent Application Publication No. Hei 3-81022, and Patent Document 2 is Japanese Unexamined Patent Application Publication No. Hei 7-77231.